Mobile computing devices have been developed to increase the functionality that is made available to users in a mobile setting. For example, a user may interact with a mobile phone, tablet computer, or other mobile computing device to check email, surf the web, compose texts, interact with applications, and so on. One challenge that faces developers of mobile computing devices is efficient power management and extension of battery life. For instance, a host device has limited availability of power from an internal battery. In some scenarios, a device may obtain supplemental power from an external battery. However, internal and external batteries associated with traditional devices are typically charged and managed separately. One consequence of this approach is that availability to use the host device apart from an external battery (or other power source) may be limited by the initial charge state of the internal battery. Additionally, a user may have to carry and use multiple different chargers to maintain internal and external batteries, which is cumbersome and inefficient.